Multishell Fullerenes Research Articles

Fullerenes and Buckyonions in the Interstellar Medium

We show that photoabsorption by fullerenes and buckyonions (multishell fullerenes) explain the shape, width, and peak energy of the most prominent feature of interstellar absorption, the UV bump at 2175 A. The predicted optical and near-infrared transitions for these molecules also offer a potential explanation for the long-standing problem of the identity of the diffuse interstellar bands. The implied ubiquitous distribution of fullerenes may also account for the anomalous galactic microwave emission detected by cosmic microwave background experiments. Comparing theoretical cross sections and astronomical data, we estimate a density of fullerenes in the diffuse interstellar medium of 0.1-0.2 parts per million, consistent with the findings in meteorites. Fullerene-based molecules appear to be a major carbon reservoir in the interstellar medium.

A theoretical model of the static polarizability of carbon buckyonions

A theoretical approach to determine the static dipole polarizabilities of carbon buckyonions is presented. The microscopic electronic structure of the system is provided by an effective one-electron model and the screening effects are treated within the random phase approximation (RPA). The particular spherical geometry of these multishell fullerenes makes possible the use of electrostatic arguments to derive a simple expression for the RPA which gives the polarizability of the buckyonion and the dipole moment induced on each shell in terms of either the screened or unscreened polarizabilities of the isolated shells. A systematic analysis as a function of the buckyonion size is performed. The relevance of an adequate microscopic description of the electronic structure is demonstrated by contrasting the results provided by two different representations of the electron motion, namely a surface electron gas and a more realistic Hückel model. A comparison between our results and those derived from classical dielectric models is also performed.

Continuously Growing Spiral Carbon Nanoparticles as the Intermediates in the Formation of Fullerenes and Nanoonions

We report the occurrence of quasispherical Archimedean spiral carbon nanoparticles and their transformation into onion-like nested multishell fullerenes. Irradiation of electron beam onto nanosized carbon particles forms spiral nanoparticles prior to transformation into onions. In situ microscopic observation reveals that the spiral-onion conversion is reversible and progresses outward from the center of a particle. A scheme is presented whereby thermodynamically most stable onion configuration is reached through the reversible transformation with the spiral intermediate playing the role of shell-adjuster. The scheme encompasses the growth mechanism of single- as well as multishell fullerene formation.

Synthesis of multishell fullerenes by laser vaporization of composite carbon targets

Multishell fullerenes are the smallest among multishell carbon clusters, such as the larger graphitic onions or multishell nanotubes. Unlike classical fullerenes, which have a cage structure and are known to have been synthesized in a variety of sizes (C60, C70, C84, C102, etc.), multishell fullerenes have a cage-inside-cage concentric structure, such as double-shell C60@C240 or triple-shell C60@C240@C560. We report on the synthesis of multishell fullerenes by laser vaporization of C60-containing composite carbon targets. Transmission electron microscopy, Raman scattering spectroscopy, and other methods were used for characterization of the product. The yield of the process reaches up to 40%, which permits production in gram amounts even in laboratory conditions.

Mechanisms involved in the formation of onionlike carbon nanostructures synthesized by ion implantation at high temperature

The origin of the formation of multishell fullerenes (carbon onions) produced by carbon ion-implantations performed at high-temperature into silver is discussed on the basis of high-resolution transmission electron microscopy observations. For low carbon fluences, one observes the formation inside the silver matrix of poorly organized carbon nanostructures the shape of which is roughly spherical. They progressively evolve towards perfect onionlike structures when the implanted carbon fluence increases. The catalytic effect of silver, which lowers the graphitization temperature of the carbon, the irradiation-induced displacements of the carbon atoms, and the effect of the temperature are proposed to be the key mechanisms that control the formation of the onionlike structures observed in such experiments.

Multishell fullerenes by laser vaporization of composite carbon–metal targets

The extension of the laser vaporization method to composite fullerene-containing carbon targets is reported. High-yield synthesis of the recently discovered multishell fullerenes, which represent a novel variety of carbon nanoclusters, has been achieved. The content of the multishell fullerenes in the deposits may reach up to 90%. The multishell fullerenes such as double-shell C 60@C 240 or triple-shell C 60@C 240@C 560 are the smallest among other multishell carbon clusters.

Formation of multishell fullerenes from vaporized carbons

Two different processes, which lead to formation of multishell fullerenes, are reported and discussed. The first process is 3000°C high temperature treatment of C 60 -containing carbon blacks. The second process is laser vaporization of composite carbon targets, containing C 60 and vapor-grown carbon fibers (VGCF). It has been shown that the laser vaporization technique allows increasing the yield up to 40%. Possible mechanisms of formation of the outer shells are discussed.

The Observation of Large Concentric Shell Fullerenes and Fullerene-like Nanoparticles in Laser Pyrolysis Carbon Blacks

It has been shown that carbon blacks produced by iron carbonyl-catalyzed CO 2 -laser pyrolysis of benzene (laser pyrolysis carbon blacks) are characterized by a two-level nanostructure, i.e., they consist of amorphous carbon nanoparticles 30-40 nm in size and fullerene molecules where the fullerenes are predominantly represented by C 60 . Heat treatment of the blacks at 3000°C causes restructurization with the appearance of fullerene-like multishell nanoparticles of ∼20 nm in size, higher fullerenes, and multishell fullerenes. Unlike classical fullerenes, which have a cage structure and are known to have been synthesized in a variety of sizes (C 60 , C 70 , C 84 , C 102 , etc.), multishell fullerenes have a cage-inside-cage structure. Direct transmission electron microscopy observation of the cage-inside-cage clusters shows the occurrence of at least three varieties: two-shell 14-A-sized C 60 @C 240 , two-shell 20-A-sized (C 240 @C 560 ), and also three-shell 20-A-sized (C 80 @C 240 @C 560 ).

Nanostructure of laser pyrolysis carbon blacks: observation of multiwall fullerenes

A study of the nanostructure of both as-produced and thermally treated laser pyrolysis carbon blacks which comprise unusual types of nanoparticles and fullerenes is reported. It has been shown that those blacks are characterized by two-level nanostructure, i.e. they consist of amorphous nanoparticles 30–40 nm in size and C60 clusters. Heat treatment at 3000°C causes restructurization with appearance of fullerene-like multishell nanoparticles of ∼20 nm size, higher fullerenes and multishell (cage-inside-cage) fullerenes. Transmission electron microscopy observation showed the occurrence of three different cage-inside-cage clusters: two-shell 1.4 nm size (C60@C240), two-shell 2.0 nm size (C240@C560) and three-shell 2.0 nm size (C80@C240@C560).

Carbon Onions as Possible Carriers of the 2175 A Interstellar Absorption Bump

We have studied the ultraviolet (UV) optical response of various hollow and filled spherical multishell fullerenes (commonly called carbon onions) in the wavelength region of the carbon π-plasmon excitation. Our theoretical approach, which follows a recently proposed growth model, allowed us to investigate the modification of the electronic properties of these clusters brought about by a material (for example, diamond) filling the inner cavity and by a coating layer (for example, water). We found that coated onion particles have optical properties consistent with the UV interstellar dust absorption data, including the constant position of the absorption maximum associated with a large variation of the resonance width.

Procedure to Determine the Structure of Three-Horned Multishell Fullerene

Abstract Fullerenes have many families such as simple ball-shaped fullerenes, nanotubes, and onions. Additionally torus, Y-shaped particle, and graphitic network with periodic holes or dimples have been theoretically anticipated. The presence of various shapes in fullerenes is mainly attributed to the combination of five-membered and seven-membered rings in addition to six-membered rings composing ordinary graphite crystal. The five-membered rings are necessary for positive curvature of the fullerenes, while the seven-membered rings for negative curvature. Experimentally, the negative curvature has been restricted so far to the joint between cone and tube in nanotubes and the spiral tubes. We have found a new type of multishell fullerenes with negative curvature which consist of three horns protrude into three-fold symmetric directions, referred as three-horned multishell fullerene (THF) in this report, using a high resolution transmission electron microscope (TEM). Here, we first describe the formation briefly and secondly concerned with procedure to determine the structure of the THF.

Collective excitations of multishell carbon microstructures: Multishell fullerenes and coaxial nanotubes.

\ensuremath{\sigma} and \ensuremath{\pi} plasmons in coaxial carbon nanotubes and multishell fullerenes are modeled in analogy with coupled collective excitations in finite, layered, two-dimensional-electron-gas, planar semiconductor superlattices. The curvature of the surface of these complex carbon clusters plays an important role in shaping the dimensionality (one dimensional, two dimensional, or three dimensional) of the plasmons. Direct crossover from a one-dimensional to a three-dimensional regime is found under readily fulfilled conditions for carbon nanotubes in the case of small finite longitudinal momentum transfer \ensuremath{\Elzxh}q, while for q=0 bulk graphitic plasmons fail to develop. For large q, a two-dimensional behavior is found. The case of multishell fullerenes resembles in all instances the q=0 behavior of carbon nanotubes. Such behavior correlates with the observed systematic redshift of the strong interstellar absorption band as compared to the \ensuremath{\pi} plasmon of bulk oriented graphite (i.e., the 5.7 eV position of the former compared to the 6.2 eV energy of the latter). Furthermore, in the case of \ensuremath{\pi} plasmons in carbon nanotubes, a special surface mode can develop for large q, due to the difference in the values of the dielectric constants between the graphitic structures and the surrounding medium. \textcopyright{} 1996 The American Physical Society.

96/01497 On the ultraviolet spectrum of multishell fullerenes and its role as possible component of interstellar dust

96/01497 On the ultraviolet spectrum of multishell fullerenes and its role as possible component of interstellar dust

Dielectric model for giant fullerenes

The ultraviolet polarizability of spherical and cylindrical multishell fullerenes is considered in a continuum macroscopic dielectric framework and within a discrete dipole approximation. We studied the position and the shape variation of the collective π-plasmon excitation as a function of the shape of the hollow cluster. The results are compared with available experimental data.

On the Ultraviolet Spectrum of Multishell Fullerenes and Its Role as Possible Component of Interstellar Dust

Abstract The origin of the ultraviolet (UV) interstellar dust absorption is still uncertain. We have studied the shape dependance of the UV absorption of spherical and cylindrical (tubular) single- and. We shown that these materials are possible interstellar carriers of the UV band.

Theoretical studies of multishell fullerenes.

In this paper two types of multishell fullerenes have been investigated. They are the multishells of the concentric circumspheres of polyhedra {ital C}{sub {ital n}} ({ital I}{sub {ital h}}, {ital n}=60{ital k}{sup 2}) and {ital C}{sub {ital n}} ({ital I}{sub {ital h}}, {ital n}=180{ital k}{sup 2}), respectively, where {ital k} is the sequence of positive integers 1,2, up to {ital L}, and {ital L} is the number of shells. The electronic structures of the multishell fullerenes have been calculated with the values of {ital k} from 1 to 25 for the first type, and the values of {ital k} from 1 to 14 for the second type. The van der Waals energies and the Gibbs functions for the formation of multishell fullerenes from the isolated shells have also been derived.

Interstellar graphitic particles generated by annealing of nanodiamonds and their relation to the 2175 A peak carrier

view Abstract Citations (30) References (37) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Interstellar Graphitic Particles Generated by Annealing of Nanodiamonds and Their Relation to the 2175 Angstrom Peak Carrier Ugarte, Daniel Abstract Since the discovery of the 2175 A absorption bump, this peak has been associated with graphitic particles. Recent development of carbon cluster physics revealed a very robust nanometric carbon structure: onion-like graphitic particle (multishell fullerene). On the basis of laboratory data, we analyze the possible generation of this kind of cluster in interstellar space. In particular, we speculate that tiny nanodiamonds are formed by a chemical vapor disposition (CVD) process in the circumstellar environment and are subsequently thermally annealed to concentrically shelled graphitic particles. These particles have important implications for the UV bump carrier grains, as they would account for observational contraints requiring a narrow shape distribution and also that hydrogen must be involved in the formation mechanism Publication: The Astrophysical Journal Pub Date: April 1995 DOI: 10.1086/187842 Bibcode: 1995ApJ...443L..85U Keywords: Annealing; Graphite; Interstellar Matter; Stellar Envelopes; Ultraviolet Absorption; Ultraviolet Spectra; Vapor Deposition; Chemical Composition; Hydrogen; Red Shift; Astrophysics; ISM: DUST; EXTINCTION; ULTRAVIOLET: ISM full text sources ADS |

Onion-like graphitic particles

Nanometric graphitic structures (fullerenes, nanotubes, bucky-onions, etc.) form in different harsh environments (electric arc, electron irradiation, plasma torch). In particular, the onion-like graphitic particles may display a wide range of structures, going from polyhedral to nearly spherical. High-resolution electron microscopy is the primary tool for studying these systems. On the basis of HREM observations, we discuss the energetics and possible formation mechanism of these multi-shell fullerenes. The better understanding of the underlying processes would allow the development of an efficient production method.

Graphitic Nanoparticles

Pure carbon materials, graphite and diamond, possess a wide array of interesting physical properties, and so attract a large spectra of interests and applications. Carbon microparticles (carbon black) and carbon fibers are widely used in practical applications including common materials (paints, inks, polymers, etc.) and high-performance composite materials.Carbon displays a remarkably rich and complex chemical behavior (three different possible hybridizations: sp1, sp2, and sp3). In particular, the covalent carboncarbon bond is one of the strongest in nature, and induces a high melting temperature (> 4000°C). The phase changes associated with unusually high temperatures and pressures as revealed in the carbon phase diagram, and the fact that the solid sublimates at low pressures before melting, lead to many experimental difficulties in the study of high-temperature properties of carbon materials. Experiments must therefore rely on transient melting, for example, laser vaporization or arc-discharge heating. This explains why fullerenes and related graphitic structures have only recently been discovered.From a fundamental point of view, the discovery of fullerenes has introduced new ideas about how carbon atoms bond. The curvature and closure of graphitic surfaces has become a standard concept in carbon chemistry, and recently a wide range of structures formed by curved graphitic networks has been observed. A surprising aspect of fullerene research is that these novel graphitic structures were found in well-known experiments, and that they had been overlooked for so many years.This article will describe recent progress in the generation and physical characterization of graphitic nanoparticles, or multishell fullerenes. The lack of an efficient method for producing, as well as a method for purifying these particles makes it difficult to characterize them and to develop possible applications.

Modifying the buckyball

Structural and electronic properties of carbon clusters, in particular the C 60 “buckyball” molecule as well as structurally and chemically modified fullerenes, are calculated using a combination of predictive ab initio techniques and parametrized total energy schemes. These calculations indicate that single- and multi-shell fullerenes are the most stable C n isomers at T = 0 for n < 20. More open structures are favored by entropy at higher temperatures. Upon interaction with donor elements, C 60 molecules form stable M@C 60 endohedral complexes; analogous acceptor-based complexes are unstable. Solid C 60 reacts with alkali metals and forms a stable intercalation compound which shows superconducting behavior. The relatively high value of the critical temperature for superconductivity can be explained quantitatively within the Bardeen-Cooper-Schrieffer formalism.